Method of generating gas



Oct. 28, 195s A. ZLETZ ET AL METHOD OF GENERATING c s' Filed Dec. 9, 1953 O X/DIZER INVENTORS Alex 2/6 000 R. ()armodyv Walter H. Bufcher temperatures.

Un fi d ates. P ten m 7 8. METHOD or GENERATING GAS Alex Zletz, Park Forest, Don R. CarmodyfCreteQa'nd Walter W. Butcher, Chicago, Ill., assignors to Standard Oil Company, Chicago, Ill., ac o'rpora'tion of ludianaj 1 Application December 9', i953, Serial-No. 391.018 f 4 Claims. (cl. so -35.4

This invention relates to gasjgeneration and rocket propulsion. More particularly the inventionurelates-to a liquid rocket fuel which is suitable for'use at very low Bipropellant rockets have assumed a larger and larger place in the military andcommercial fields both in missiles and in the assisted take-off. of aircraft; -In the bipropellant rocket a liquid fueland a liquid oxidizer are injected separately and substantially simultaneously-into the combustion chamber of the; rocket'- mot or;. the fuel and oxidizer ignite hypergolically or arei'gnited by an external system such as asparkplug and burntoform a large volume of gases as high temperaturfib hese' gases are passed from the combustioncham ber .by-wayof'; an exitorifice.. j I; z

A hypergolic fuel-oxidizer system is preferred because atmospheric.temperatures.,. 1

an ancillary ignitingsystem is thereby eliminated. In

general the hypergolic activity of liquid fuelsgand nitric acid oxidizers decreases markedly with lowering .;of .the temperature of the fuel and oxidizer. An airto.-a l'-missile usually is exposed to the extreme cold of high. altitudes for a period long enough to substantially attain atmospheric temperature. At the altitude now commonly utilized by. military aircraft, temperatures. (lathe-order of about-65 F. arecustomary andv +100? E. is not uncommon. z

Not only must the fuel have a melting point below about 65 F., but also the .fuel should have a viscosity low enough to flow readily through the-fuel lines: at very low atmospheric temperatures, i. e.,. about.. 65? F. or lower. H 1 i I .1

The presently known liquid rocket-fuels. which fulfill these requirements are extremely expensive; for most of these the price is quoted in dollars per pound. More ,eco-

nomical fuels which meetthese severe requirements-are desired in order to expand the field of usefulness of rocket-propelled vehicles. g 1 Y 1. An object of this invention is a rocket fuel which is suitable for use at very low atmospheric temperatures, e., below about 65 F. Another object is a: liquid rocket fuel which is suitable for use at very low atmospheric temperatures and which is less expensive than the presently known fuels. Still anotherobject is a method of gas generation by the hypergolic reaction of a nitric acid oxidizer and a liquid rocket fuel at very low atmospheric Yet another object is a method of rocket propulsion by the hypergolic reactionof the nitric acid oxidizer and a liquid rocket fuel at very low atmospheric temperatures. v I

It has been found that a compositioneonsistingessen- ,tially of at least about 25 volume percent of a phosphine and the remainder .a liquid hydrocarbon 1 mixture which boils from about 250 to about 400 F. and which is rocket fuel with nitric acid oxidizersatvery lowatmospheric temperatures.

2,857,738 Patented Oct. 28, 1958 The phosphine component is selected from at least one member selected from the class consisting of;

A. Monoaliphatic phosphines which contain not more than 16 carbon atoms.

B. Dialiphatic phosphines which. contain not more than 20 carbon atoms and wherein each aliphatic group contains not more than 16 carbon atoms.

C. Trialiphatic phosphines which contain. not more than 9 carbon atoms and wherein each aliphatic group contains not more than 6 carbon atoms.

The above-defined fuel composition has a satisfactory hypergolic activity with certain nitric acid oxidizers, hereinafter defined, when the fuel'and the oxidizer at the moment of contact in the gas generationchamber or the rocket motor are at a temperature below about 1-65 F.

Several methods are known for the preparation of the aliphatic phosphines, e. g., the method of W. C. Davies and W. J. Jones as described in J. Chem. Soc. (London), p. 33 (1929); also, that of W. C. Davies in J. Chem. Soc. (London), p. 1043 (1933). Both of these methods involve the Grignard reaction. However, it is .preferred to use the method described in U. S. Patent 2,584,112 which involves the reaction of phosphine,'PH and an olefin.

V The products from all of these methods of preparation contain minor amounts of impurities. These impurities have a favorable effect on the freezing pointrof the aliphatic phosphines and appear to have no substantial adverse eifect on hypergolic activity. It has also been found that the aliphatic phosphines whichhave been oxidized to a minor extent, e. g., 4 or 5%; are useful as hypergolic fuels. It is intended to include within the scope of theinvention the use of aliphatic phosphines which contain minor amounts of impurities resulting from the preparation thereof and also those whichjcontain minor amounts of oxidation product resulting from the oxidation of the aliphatic phosphine. Certain monoaliphtic phosphines. dialiphatic phosphines, trialiphatic phosphines and mixtures. thereof are useful for the purposes of the invention. The term aliphatic as used herein is intended to include hydrocarbon groups selected from the class consisting of parafiins, olenfins, and alicyclics. In the case of alicyclic groups, the group may be attached to the phosphorus -either through a ring carbon atom or through a side chain carbon atom. It has been found that the highly branched aliphatic groups have desirably lower freezing points than the straight chain or slightly branched groups. 'It is. preferred to use branched aliphatic groups. The presence of unsaturated linkages in the aliphatic group improves the hypergolic activity. Thus a particularly useful phosphine has a highly branched aliphatic group with one or more unsaturated linkages.

The hypergolic activity of the various aliphatic phosphines is dependent upon the number of aliphatic groups, upon the total number of carbon atoms contained in the aliphatic phosphine, and upon the number of. carbon atoms contained in each of the aliphatic groups. In order to obtain a fuel which is usable at temperatures as lowas F., it is necessary that the monoaliphatic phosphines contain not more than 16 carbon atoms. The phosphines which contain two aliphatic substituents, i. e., dialiphatic phosphines, must contain not more than 20 carbon atoms in the molecule and each aliphatic group must not contain more than 16 carbon atoms Thus a dialiphatic phosphine which contains a 16 carbon atom side chain must not contain more than 4 carbon atoms in the second side chain. The completely substituted phosphines, i. e., trialiphatic phosphines, must not contain more than 9 carbon atoms in the molecule and no aliphatic group must contain more than 6 carbon atoms.

Thus a trialiphatic phosphine which contains a 6 carbon 'atom side chain will contain only a methyl and ethyl substituent as the other aliphatic groups.

contain not more than 12 carbon atoms; and dialiphatic phosphines which contain not more than 20 carbon atoms and wherein each aliphatic group contains not more than 12 carbon atoms.

The rocket fuel composition of this invention contains as the other component a liquid hydrocarbon mixture which boils between about 250 and about 400 F.-

below about 50 p. s. i. a., and at contact times from about 0.05 to seconds, usually below about 2 seconds. Suitable feeds are ethane, propane, butane, propylene, butylene, naphthas, gas oils and other hydrocarbons which can be -It is preferred to use monoaliphatic phosphines which i been alkylated with cycloolefins and/or cyclodienes are thought to he present When the ASTM end point of vaporized at the temperature of pyrolysis without an excessive amount of coke formation. The high temperature vapor phase pyrolytic reactionis normally used for the production of olefinic gases, such as, ethylene and propylene; and for the production of aromatic hydrocarbons, such as, benzene, toluene and xylene. In general, at a given temperature, the longer the contact time the greater the amount of aromatics produced. The gases from the cracking reaction are rapidly cooled, usually by quenching with water, to a temperature of about 400 F. A .viscous tarry material condenses out of the gases during the quenching. The gases from the quenching operation are compressed and cooled; a liquid material which boils between about 100 and 400 F. condenses out of the gases during this compression-cooling step. This liquid is "commonly known as dripolene. The amount of tar and dripoleneproduced is dependent upon the feed, temperature, contact time and the pressure. The preferred operating conditions for the production of the remainder is thought to consist of other condensed-benzenen'ng compounds. This t-ar is non-hypergolic with nitric acid oxidizers at atmospheric temperatures. The presence of tarry material in the dripolene should be avoided.

The presence of a considerable amount of conjugated unsaturation in dripolene is evidenced by maleic anhydride values about about 60 and by the ease with which the dripolene can be resinified when using catalysts such as AlCl or BF Dripolene has never been completely analyzed because of its complexity. However, some of the components boiling below about 300 F. have been identified. These comprise minor amounts of propane, butane and pentane; some propylene and butylenes; appreciable amounts of butadiene; cyclopentadiene and cyclohexadiene in fair amounts; cyclopentane and cyclopentene are also present; about one-half of the dripolene consists of benzene, toluene, xylene and ethylbenzene;

I styrene is present in appreciable amounts.

The material boiling above 300 .F. is known to contain some dicyclopentadiene; the remainder is thought to consist of higher boiling alkylated benzenes, condensed cycloolefins and cyclodienes; in addition aromatics which have the dripolene is above about 400 F., a minor amount of naphthalene is usually also present. The presence of naphthalene is detrimental to the freezing point of the dripolene and normally the dripolene is cut to an end point of about 375 F. to eliminate naphthalene.

While the high temperature pyrolysis of hydrocarbons, such as, ethane, propane, gas oil, etc., is the preferred sourceof the mixture of this invention, other sources are available. These other sources produce in abundant supply a light oil fraction ,which contains a hypergolic fuel equivalent to thatobtained from dripolene. The more common sources are related to the carbonization of coal. A very good source is thelight oil obtained from the carbonization of coal at low temperatures, i. e., from about 1250 to 1600 F. Appreciable amounts are obtainable from the light oil derived from the so-called high temperature carbonization of coal for the'production of metallurgical coke. An excellent source is the light oil derived from the production of coal gas, particularly when this process is carried out at from about 1250 to 1650 F. Y a I Still another source is the drip oil obtained from the manufacture of producer gas when using coal. An excel len source is the drip oil obtained in the manufacture of carbureted water gas.

It is to be understood that the above list of sources of the fuel ofthis invention is not complete and that there are other lesser known sources. It is intended that the descriptivephrase high temperature pyrolysis of hydrocarb'ons-includes-all the processes operating at a temperature of at least about 1250 F. to produce a liquid hydrocarbon oil from which can be distilled a fraction containing polyolefinic linkages and having a maleic anhydride value of at least about 20 and boiling from at least about 250 to about 400 F., preferably from about 270 to about 375 F. I

' By way'of an example, a particular liquidhydrocarbon mixture suitable for use in the invention is described below. In this particular example the feed to the pyrolysis consisted of ethane, 8 volume percent; propane, and butanes, 2%. The pressure at the inlet to the furnace was about 40 p. s. i. g. and the exit pressure was about 11 p. s. i. g. The transfer line temperature was 1520 F. and the contact time in the high temperature zone in the furnace was about 0.2 hecond. The hot gases were quenched with water to eliminate tar. The dripolene fraction amounted to 3 weight percent of the feed. The non-condensible product contained about 25 volume percent of ethylene and about 11 volume percent of propylene. The dripolene was characterized as follows:

A sample of the dripolene was analyzed by conventional techniques for the presence of individual compounds or groups of closely related compounds. There are listed below the more or less positively identified "components and the approximate amount present in "volume percent. i

Compound: 1 Volume percent Propane and propylene 0.7 Isobutane 0.1 Butylenes.- 2 n-Butane Y 0.4 Butadiene i 4 Pentane 1 0.4 Pentadiene and cyclopentadiene 8 Pentene and cyclopentene 6 Benzene g 35 Toluene 8 Xylenes 5 Styrene t 3 Dicyclopentadiene 5 A :rocket fuel consisting essentially of at least about 20 volume percent of the defin'ed aliphatic phosphines and the remainderof the definedliquid hydrocarbon mixture boiling from about 250 to about 400 F., is characterized "by a suitably shortignition delay with certain nitric acid oxidizers hereinafter defined. The composition is characterized "by a very low viscosity at very low atmospheric temperatures, i. e., below 65 F. and even at 100 F. The melting point of the composition makes it very suitable for use at very low atmospheric temperatures.

A composition consisting essentially of between about 50 and 70 volume percent of the defined liquid hydrocarbon mixture boiling .from about 250 to about 400 F. and the remainder a monoaliphatic phosphine containing not more than 12 carbon atoms is particularly :suitable :for very low temperature operation because of its hypergolic activity with red.fuming nitric acid at these temperatures. This particular composition is preferred with ignition delays on theorder of 50 milliseconds are desired at temperatures on the order of 100 F.

The rocket fuel composition of the invention is hypergolic at ordinary temperatures, i. e., about 75 F., with most nitric acid oxidizers. At temperatures on the order of F. it is hypergolic with nitric acid oxidizers containing as much as weight percent of non-acidic materials. These non-acidic materials may be water or pour point depressors such as potassium nitrite or sodium nitrate. At very low atmospheric temperatures such as -65 F., the nitric acid oxidizers are selected from the class consisting of red fuming nitric acid, nitric acidoleum mixtures and nitric acid-alkanesulfonic acid mixture. The nitric acid-oleum mixtures consist of White fuming nitric acid and oleum, for example, an 80:20 mixture. The nitric acid-alkanesulfonic acid mixtures may consist of mixtures of WFNA and methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, etc. It is preferred to use red fuming nitric acid containing at least about 16% of N 0,; as the oxidizer at very low temperatures. Only enough oleum or alkanesulfonic acid is present to give a freezing point somewhat lower than the desired initial temperature of operation.

A composition having hypergolic properties suitable for use at very low atmospheric temperatures with nitric acid oxidizers is obtained by blending the defined aliphatic phosphine and a liquid hydrocarbon mixture derived from the light oil product, boiling from about 100 to about 400 F, of the high temperature pyrolysis of hydrocarbons at a temperature of at least about 1250 F. by chilling said oil to a temperature of about 70 F., or lower, and separating said mixture from solid materials.

Example The method of U. S. 2,584,112 was used to react diisobutylene and PB The narrow boiling fraction corresponding to the monoalkyl phosphine containing eight carbon atoms was used in these tests.

Cit

.measurement of the delay in milliseconds. delays were determined by cooling the fuel and the oxidiz- ,which contained about 2 weight percent of water.

""The' HF -D" used in this example' ha'd' the following properties:

H/C atomic ratio 1.1 8 Heat of combustion, B. t. u./lb 1 8,249 Bromine number 112 Maleic anhydride value 2418 Meltingpoint, :F. -a -1'00 Specific gravity +70 F L940 Viscosity, centistokes +70 F 1.714

ASTM distillation, percent distilled:

IBP 252 10 6 "20 298 30 309 40 3 20 50 32 9 60 v 338 70 347 so. 35 9 90" 388 FBP 42 8 The ignition delay is defined as the time between the mixing of the fuel and the oxidizer and the appearance of a visible flame. The ignition delays in this example were determined by means of an apparatus which permitted the The ignition .er separately to the desired temperature. The oxidizer in the +7-5 F. .experiment was white fuming nitric acid The other experiments were carried out using red fuming nitric acid containing 22 weight percent of N 0 The test blend contained .30 volume percent of the mono (octyl) phosphine and 70 volumepercent of the HFD..,- Ih-e data derived in these tests are set out below.

[Ignition delaymilliseconds] mono F. (octyl) HF-D Blend phosphine The data further show that the ignition delays of the blend are relatively unaffected by temperature to a temperature of about F. Considering the extremely long delay of the HFD hydrocarbon alone, the independence of the ignition delays of the test blend with temperature is most surprising.

For air-to-air missile usage an ignition delay of as much as 100' milliseconds is considered suitable. More desirably the ignition delay should be on the order of 50 milliseconds. It is preferred that the ignition delay should be nearly instantaneous. It is indicated that a rocket fuel which has an ignition delay of about 50 milliseconds or less at temperatures on the order of l00 F., is obtainable from a blend containing at least about 30 volume percent of monoaliphatic phosphine having not more than 12 carbon atoms and about volume percent of the defined liquid hydrocarbon mixture.

By way of illustration the composition of this invention is applied to the propulsion of an air-to-air missile. The

' annexed figure which forms a part of this specification which regulates the flow of pressure beyond valve 13.

valves 22 and 29.

gas to maintain a constant From valve 13 helium is passed through lines 14 and 16 into vessel 17 and simultaneously through line 18 into vessel 19.

Vessel 17 contains the oxidizer. Helium pressure forces the oxidizer out of vessel 17 through line 21 to valve 22. Valve 22 is a solenoid actuated throttling valve. Suitable electrical lines connect valve 22 to an electrical source and operating switch (not shown) at the control panel of 'the aircraft. The oxidizer is passed through line 23 and injector 24 into combustion chamber 26. Combustion chamber 26 is provided with an outlet nozzle 27.

.Vessel 19 contains the fuel. Vessels 17 and 19 are 'constructed to withstand the high pressure imposed by the helium gas; The gas pressure forces fuel from vessel injector 32 into combustion chamber26.

Valves 22 and 29 are of such a size and setting that a predetermined ratio of oxidizer-to-fuel is passed into combustion chamber 26. Injectors 24 and 32 are so arranged thatthe streams of oxidizer and fuel converge and contact each other forcibly, resulting in a very thorough intermingling of the fuel and the oxidizer.

The missile is launched by activating the solenoids on In this illustration 4.5 lbs. of 22% RFNA are introduced into combustion chamber 26 per pound of fuel. Herein the fuel consists of 35 volume percent of a monoalkyl phosphine containing carbon atoms and 70 volume percent of the defined liquid hydrocarbon mixture boiling between about 275 and 375 F. The oxidizer and the fuel react almost instantaneously upon contact in the combustion chamber; a large volume of very hot gas is produced in the combustion chamber,

. which gas escapes through orifice 27. The reaction from this expulsion of gas drives the missile toward its target.

Thus having described the invention, what is claimed is:

' (II) a hypergolic liquid fuel consisting essentially of (1) betweenabout' and volume percent, based on fuel, of aliquid hydrocarbon mixture boiling over the range from about 250and400 R, which mixture is derived from the liquid product of the pyrolysis, in the vapor phase of a member of the-class consisting of ethane, propane, butane, propylene, butylene, naphthas and gas oils, at a temperature between about 1250 and 1800 F., at

a cracking zone pressure of not more than p. s. i. a.

and for a cracking zoneresidence time between about 0.05 and 5 seconds, by separating a'liquid product from other cracking products and-distilling said liquid product to obtain said mixture and (2) the remainder essentially mono- (octyl)phosphine, in an amount and at a rate sufficient to initiate a hypergolic reaction with and to support combustion of the fuel.

2. The method of claim 1 wherein said nitric acid oxidizer is red fuming nitric acid.

3. The method of claim 1 wherein the member of said class is propane.

4. The method of claim'3 wherein said mixture boils over the range from about 270 to about 375 F.

References Cited in the file of this patent UNITED STATES PATENTS Hess et al Feb. 21, 1956 

1. A METHOD OF GENERATING GAS, WHICH METHOD COMPRISES INJECTING SEPARATELY AND ESSENTIALLY SIMULRANEOUSLY INTO THE COMBUSTION CHAMBER OF THE GAS GENERATOR (1) A NITRIC ACID OXIDIZER SELECTED FROM THE CLASS CONSISTING OF WHITE FUMING NITRIC ACID AND RED FUMING NITRIC ACID AND (II) A HYPERGOLIC LIQUID FUEL CONSISTING ESSENTIALLY OF (1) BETWEEN ABOUT 50 AND 70 VOLUME PERCENT, BASED ON FUEL, OF A LIQUID HYDROCARBON MIXTURE BOILING OVER THE RANGE FROM ABOUT 250* AND 400*F., WHICH MIXTURES IS DERIVED FROM THE LIQUID PRODUCT OF THE PYROLYSIS, IN THE VAPOR PHASE OF A MEMBER OF THE CLASS CONSISTING OF ETHANE, PROPANE, NUTANE, PROPYLENE, BUTYLENE, NAPHTHAS AND GAS OILS, AT A TEMPERATURE BETWEEN ABOUT 1250* AND 1800F., AT 